A double end-capped ethylene glycol ether refers to the ethylene glycol ether obtained by substituting hydrogen atoms in the two terminal hydroxyl groups of ethylene glycol with hydrocarbyl groups. The double end-capped ethylene glycol ether has no active hydrogen, and has the characteristics of strong chemical stability, low flow point, little change in viscosity-temperature, good heat resistance, strong acid-base stability, good emulsifying capability, low foam, strong lipophilic capability, good coking resistance, and lower viscosity and density. Therefore, a double end-capped polyethylene glycol ether has a wide range of applications in the fields of high-speed spinning oils, low-foaming detergents, food processing, bio-fermentation, and the like.
The preparation methods of the double end-capped ethylene glycol ether mainly comprise a synthesis method using halogenated hydrocarbons and sodium alcoholates (Williamson synthesis) and a direct etherification method. Williamson synthesis means that an ether is produced by reacting a halogenated hydrocarbon with a sodium alcoholate under anhydrous conditions, which has disadvantages of serious pollution, dangerous operation, and lower economical efficiency. The direct etherification method refers to a method of direct etherification using an ethylene glycol or an ethylene glycol monoether and a monohydric alcohol or a monohydric alcohol ether. For instance, ethylene glycol dimethyl ether may be prepared from ethylene glycol monomethyl ether and dimethyl ether by using an anion exchange resin as a catalyst (U.S. Pat. No. 4,321,413); or ethylene glycol dimethyl ether may be prepared from ethylene glycol and methanol by using a perfluorinated sulfonic acid resin as a catalyst (U.S. 2004/0044253). The catalysts used in these methods have low yield, selectivity and longevity, and it is difficult to regenerate the resin catalysts. In addition, these methods may easily produce a large amount of by-products such as 1,4-dioxane, double end-capped polyethylene glycol ethers, and the like.